Transforming growth factor-b (TGF-beta) is a negative regulator of prostate growth via its ability to inhibit cell proliferation and induce apoptosis in epithelial cells. Evidence indicates that in prostate cancer an increase in epithelial TGF-beta expression is paralleled by loss of expression of its membrane receptors TbetaRI and TbetaRII. The long-term goal of the proposed studies is to identify the interplay between the androgen axis and TGF-beta signaling pathways during prostate tumorigenesis. Our recent studies demonstrated that restoration of expression of the functional TbetaRII receptor in human prostate cancer cells LNCaP that are resistant to TGF-beta, leads to TGF-beta sensitivity and suppression of tumorigenic growth via cell cycle arrest and apoptosis induction. In this proposal we will use this model of hormone-sensitive TGF-beta responsive prostate cancer cells to explore the molecular mechanism underlying the dysfunctional TGF-beta signaling pathway in prostate tumorigenesis. In Specific Aim 1 we will determine the ability of androgens to affect the action of TGF-beta on prostate cancer cell growth as linked to deregulation of cell cycle (cdk inhibitors) and apoptosis induction (caspases, bcl-2). The effect of androgens on TGF-beta mediated suppression of in vivo tumorigenic growth of LNCaP TbetaRII cells will be determined using orthotopic injections. In Specific Aim 2 using transfections and co-immunoprecipitation approaches we will investigate the functional involvement of the Smad intracellular effectors of TGF-beta in transducing the apoptotic signals to the nucleus. In Specific Aim 3 the interaction between the androgen receptor (AR) and TGF-beta signaling pathways in LNCaP TbetaRII prostate cells will be characterized using immunoprecipitation assays. These studies will establish: a) that androgens contribute to the impairment of TGF-beta signaling in prostate cancer cells; and b) the significance of defects in post-receptor intracellular mediators of TGF-beta signal, the Smads, in the development of hormone-resistance in prostate cancer.